Protective helmet



FIG. 1 is a front view of a protective helmet showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a lower left perspective view thereof.

The broken lines in the drawings depict portions of the protective helmet that form no part of the claimed design. 

CLAIM The ornamental design for a protective helmet, as shown and described. 